Performance and Process Parameter Specification for Foamed Silicone Rubber Rolls

Performance and Process Parameter Specification for Foamed Silicone Rubber Rolls

Foamed silicone rolls are categorized into three types: closed-cell, open-cell and mixed-cell. Dominant production processes include continuous extrusion foaming (preferred for mass roll production), liquid coating foaming and compression molding followed by slicing. They are widely applied in new energy battery sealing, electronic cushioning, equipment thermal insulation and automotive shock absorption.

I. Key Physical Performance Parameters (GB, ASTM D3574 / ASTM D1056 Standards)

1. Basic Dimension Specifications

2. Density & Hardness (Core Selection Index)

• Density: 150\700 kg/m³ (0.15\0.7 g/cm³)
Extra soft grade: 150~250 kg/m³; General grade: 300~450 kg/m³; High-density rigid foam: 500~700 kg/m³

• Shore Hardness (Shore C): 8~55C. Hardness decreases with lower density: Extra soft foam 8\15C, general grade 20\40C, high-load grade 40~55C.

3. Mechanical Properties

4. Thermal Resistance, Flame Retardancy & Electrical Properties

1. Temperature resistance: Long-term stable service from -60℃ to 200℃; instantaneous peak tolerance 250~300℃. No low-temperature embrittlement or high-temperature melting/shrinkage.

2. Flame retardancy: Standard UL94 V-0; Halogen-free low-smoke HF-1 grade for power battery applications via aluminum hydroxide filler modification.

3. Electrical property: Volume resistivity ≥1×10¹² Ω·cm, dielectric constant 1.3~1.6 with excellent insulation; conductive version available via carbon black doping.

5. Cellular Structure Parameters

• Closed-cell: Cell size 30~100 μm, closed-cell ratio ≥85%, ideal for waterproof sealing, thermal insulation and load bearing.

• Open-cell: Cell size 80~200 μm, open-cell ratio ≥70%, suitable for air permeability, sound absorption and oil absorption cushioning.

• Mixed-cell: 50%~70% closed-cell ratio, balances sealing and cushioning performance.

II. Production Process Parameters (Continuous Extrusion for Roll Production, Mainstream Technology)

(1) Formulation Parameters: Chemically Foamed HTV Solid Silicone & Addition-Cured Liquid LSR

1. Solid Mixing Formula (Peroxide + ADC Chemical Foaming)
Base methyl vinyl silicone rubber: 100 phr; Reinforcing silica: 30~60 phr;
DCP crosslinker: 0.8~1.8 phr; ADC foaming agent: 3\12 phr (foaming expansion ratio controlled at 2\7 times);
Auxiliaries (flame retardant / color masterbatch / silicone oil): 5~20 phr as required.

2. Liquid Addition System (A/B 1:1 Mix Ratio): A-component vinyl silicone oil : B-component hydrogen-containing curing agent =1:1, ppm-level platinum catalyst for in-situ CO₂ foaming.

(2) Mixing Process (Internal Mixer + Open Mill)

• Internal mixing temperature: 35~85℃, maximum limit 95℃ to prevent premature decomposition of foaming agent and abnormal cell rupture.

• Mixing duration: 8\15 min internal mixing; 5\8 times thin-passing on open mill for uniform foaming agent dispersion.

• Workshop ambient temperature: 25±5℃ to avoid premature silicone vulcanization.

(3) Extrusion Molding (Core Continuous Roll Forming)

1. Barrel staged temperature control from feed throat to die: Feed zone 40\60℃ → Plasticizing zone 70\90℃ → Die head 100~115℃.

2. Extrusion pressure: 6~12 MPa; Line speed: 2~8 m/min (lower speed for thin rolls, higher for thick rolls).

3. Die gap reserved with 2~4 times expansion allowance for post-vulcanization foaming according to finished thickness.

(4) Vulcanization & Foaming in Tiered-Temperature Tunnel Oven

Three-stage heating to avoid foam collapse or insufficient foaming:

1. Preheating zone: 120\130℃, 2\3 min, only resin softening without foaming initiation.

2. Foaming zone: 155\170℃, 3\5 min, foaming agent decomposes and releases gas to form cellular structure.

3. Crosslinking curing zone: 175\190℃, 4\7 min, silicone crosslinks and locks stable cell geometry.

• Total oven length: 20\45 m, heating rate 5\8℃/min, temperature accuracy ±2℃.

• Liquid coating foaming: Oven temp 115\140℃, curing time 8\15 min.

(5) Post-Treatment Process

1. Cooling: Air cooling with roller pressing to room temperature for dimensional stabilization and shrinkage prevention.

2. Slitting: Longitudinal cutting to specified width and rewinding into finished rolls.

3. Aging: 24~72 h room-temperature resting to release internal stress and stabilize dimensional & compression-set performance.

III. Parameter Comparison: Supercritical Physical Foaming (N₂/CO₂) vs Conventional Chemical Foaming

1. Chemical foaming (ADC blowing agent, 90% of commercial rolls): Low cost, cell size 30\200 μm, density 180\700 kg/m³, vulcanization temperature 155~190℃.

2. Supercritical physical foaming (High-end power battery grade): High-pressure N₂ injection during extrusion, ultra-fine uniform cells 10\50 μm, minimum density down to 120 kg/m³, no chemical residual with high cleanliness; equipment pressure 25\35 MPa, processing temperature 130~160℃.

IV. Modification Rules for Customized Formulation Adjustment

1. Lower density & softer texture: Increase foaming agent dosage, reduce crosslinker content and decrease oven foaming temperature.

2. Higher density, higher hardness & lower compression set: Reduce foaming agent, increase silica filler and raise vulcanization temperature.

3. Upgrade to UL94 V-0 flame retardancy: Add 25~40 phr aluminum hydroxide inorganic flame retardant.

4. Conductive foamed silicone roll: Add 15\35 phr conductive carbon black for volume resistance ranging from 10³\10⁶ Ω·cm.